There are many important, nation-wide holidays that are celebrated in the United States. Many of these are considered Federal holidays, which means employees will receive that day off, mail is not delivered and banks are closed. For a complete list of Federal holidays: http://goo.gl/7LVb.
For a complete list of holidays and observances in the U.S., you may go here: http://www.usa.gov/citizens/holidays.shtml
The United States uses nine standard time zones. From east to west they are Atlantic Standard Time (AST), Eastern Standard Time (EST), Central Standard Time (CST), Mountain Standard Time (MST), Pacific Standard Time (PST), Alaskan Standard Time (AKST), Hawaii-Aleutian Standard Time (HST), Samoa standard time (UTC-11) and Chamorro Standard Time (UTC+10).
Iowa runs on the central time zone. For a map of the time zones and what time it is right now in each one, go to http://www.timeanddate.com/time/map/
Most, but not all states, have Daylight Saving Time. You set your clock an hour forward in the spring, and move it an hour back in the fall. The idea is to have more hours of sunlight in the spring and fall. You may learn more about daylight saving, and when you are supposed to turn your clocks forward or back here: http://www.webexhibits.org/daylightsaving/b2.html